how many users can Cyrus server support? -- is 5.5 msg/sec sl ow?

[Adam Williams]

>Yes MTA is a problem. When I stop sending emails and let Cyrus IMAP finish
>the mails queued in Sendmail, I got more that 20 messages per second. 
>I have tried to use Postfix. Probebly because I didn't setup Postfix right
>(I use every thing default), I didn't get better performance than using
>Sendmail.

We use sendmail and even with LDAP maps for everything (routing,
virtuser, generics, aliases) performance is very good.

Have you tried producing a strace summary of an sendmail process when
delivering a message to see where it is spending all of its time. 
Possibly DNS is very slow?  Or your DSA if using LDAP?

I created a DNS slave and DSA replicant local on my mail server solely
for use by the local services (sendmail, nss, etc...).

You should probably head over the the sendmail lists/pages if the
problem is your MTA.